Application of oscillation for efficiency improvement of continuous ethanol fermentation with Saccharomyces cerevisiae under very-high-gravity conditions

Compared with steady state, oscillation in continuous very-high-gravity ethanol fermentation with Saccharomyces cerevisiae improved process productivity, which was thus introduced for the fermentation system composed of a tank fermentor followed by four-stage packed tubular bioreactors. When the very-high-gravity medium containing 280 g l⁻¹ glucose was fed at the dilution rate of 0.04 h⁻¹, the average ethanol of 15.8% (v/v) and residual glucose of 1.5 g l⁻¹ were achieved under the oscillatory state, with an average ethanol productivity of 2.14 g h⁻¹ l⁻¹. By contrast, only 14.8% (v/v) ethanol was achieved under the steady state at the same dilution rate, and the residual glucose was as high as 17.1 g l⁻¹, with an ethanol productivity of 2.00 g h⁻¹ l⁻¹, indicating a 7% improvement under the oscillatory state. When the fermentation system was operated under the steady state at the dilution rate of 0.027 h⁻¹ to extend the average fermentation time to 88 h from 59 h, the ethanol concentration increased slightly to 15.4% (v/v) and residual glucose decreased to 7.3 g l⁻¹, correspondingly, but the ethanol productivity was decreased drastically to 1.43 g h⁻¹ l⁻¹, indicating a 48% improvement under the oscillatory state at the dilution rate of 0.04 h⁻¹.     

Rapid solubilization of insoluble phosphate by a novel environmental stress-tolerant Burkholderia vietnamiensis M6 isolated from ginseng rhizospheric soil

We isolated and characterized novel insoluble phosphate (P)-solubilizing bacteria tolerant to environmental factors like high salt, low and high pHs, and low temperature. A bacterium M6 was isolated from a ginseng rhizospheric soil and confirmed to belong to Burkholderia vietnamiensis by BIOLOG system and 16S rRNA gene analysis. The optimal cultural conditions for the solubilization of P were 2.5% (w/v) glucose, 0.015% (w/v) urea, and 0.4% (w/v) MgCl₂·6H₂O along with initial pH 7.0 at 35°C. High-performance liquid chromatography analysis showed that B. vietnamiensis M6 produced gluconic and 2-ketogluconic acids. During the culture, the pH was reduced with increase in gluconic acid concentration and was inversely correlated with P solubilization. Insoluble P solubilization in the optimal medium was about 902 mg l⁻¹, which was approximately 1.6-fold higher than the yield in NBRIP medium (580 mg l⁻¹). B. vietnamiensis M6 showed resistance against different environmental stresses like 10–45°C, 1–5% (w/v) salt, and 2–11 pH range. The maximal concentration of soluble P produced by B. vietnamiensis M6 from Ca₃(PO₄)₂, CaHPO₄, and hydroxyapatite was 1,039, 2,132, and 1,754 mg l⁻¹, respectively. However, the strain M6 produced soluble P with 20 mg l⁻¹ from FePO₄ after 2 days and 100 mg l⁻¹ from AlPO₄ after 6 days, respectively. Our results indicate that B. vietnamiensis M6 could be a potential candidate for the development of biofertilizer applicable to environmentally stressed soil.     

1,3-Propanediol production in a two-step process fermentation from renewable feedstock

In this work, the production of 1,3-propanediol from glucose and molasses was studied in a two-step process using two recombinant microorganisms. The first step of the process is the conversion of glucose or other sugar into glycerol by the metabolic engineered Saccharomyces cerevisiae strain HC42 adapted to high (>200 g l⁻¹) glucose concentrations. The second step, carried out in the same bioreactor, was performed by the engineered strain Clostridium acetobutylicum DG1 (pSPD5) that converts glycerol to 1,3-propanediol. This two-step strategy led to a flexible process, resulting in a 1,3-propanediol production and yield that depended on the initial sugar concentration. Below 56.2 g l⁻¹ of sugar concentration, cultivation on molasses or glucose showed no significant differences. However, at higher molasses concentrations, glycerol initially produced by yeast could not be totally converted into 1,3-propanediol by C. acetobutylicum and a lower 1,3-propanediol overall yield was observed. In our hand, the best results were obtained with an initial glucose concentration of 103 g l⁻¹, leading to a final 1,3-propanediol concentration of 25.5 g l⁻¹, a productivity of 0.16 g l⁻¹ h⁻¹ and 1,3-propanediol yields of 0.56 g g⁻¹ glycerol and 0.24 g g⁻¹ sugar, which is the highest value reported for a two-step process. For an initial sugar concentration (from molasses) of 56.2 g l⁻¹, 27.4 g l⁻¹ of glycerol were produced, leading to 14.6 g l⁻¹ of 1.3-propanediol and similar values of productivity, 0.15 g l⁻¹ h⁻¹, and overall yield, 0.26 g g⁻¹ sugar.     

Fungal autolysate as a nutrient supplement for ethanol and chitosan production by <Emphasis Type="Italic">Mucor indicus</Emphasis>

Mucor indicus can be used to produce ethanol from a variety of sugars, including pentose’s. An extract of it, produced by autolysis, could replace yeast extract in culture medium with improved production of ethanol. At 10 g l⁻¹, the extract gave a higher ethanol yield (0.47 g g⁻¹) and productivity (0.71 g l⁻¹ h⁻¹) compared to medium containing yeast extract (yield 0.45 g g⁻¹; productivity 0.67 g l⁻¹ h⁻¹).     

A process for the production of ectoine and poly(3-hydroxybutyrate) by <Emphasis Type="Italic">Halomonas boliviensis</Emphasis>

The paper reports a study involving the use of Halomonas boliviensis, a moderate halophile, for co-production of compatible solute ectoine and biopolyester poly(3-hydroxybutyrate) (PHB) in a process comprising two fed-batch cultures. Initial investigations on the growth of the organism in a medium with varying NaCl concentrations showed the highest level of intracellular accumulation of ectoine (0.74 g L⁻¹) at 10–15% (w/v) NaCl, while at 15% (w/v) NaCl, the presence of hydroxyectoine (50 mg L⁻¹) was also noted. On the other hand, the maximum cell dry weight and PHB concentration of 10 and 5.8 g L⁻¹, respectively, were obtained at 5–7.5% (w/v) NaCl. A process comprising two fed-batch cultivations was developed—the first culture aimed at obtaining high cell mass and the second for achieving high yields of ectoine and PHB. In the first fed-batch culture, H. boliviensis was grown in a medium with 4.5% (w/v) NaCl and sufficient levels of monosodium glutamate, NH₄⁺, and PO₄³⁻. In the second fed-batch culture, the NaCl concentration was increased to 7.5% (w/v) to trigger ectoine synthesis, while nitrogen and phosphorus sources were fed only during the first 3 h and then stopped to favor PHB accumulation. The process resulted in PHB yield of 68.5 wt.% of cell dry weight and volumetric productivity of about 1 g L⁻¹ h⁻¹ and ectoine concentration, content, and volumetric productivity of 4.3 g L⁻¹, 7.2 wt.%, and 2.8 g L⁻¹ day⁻¹, respectively. At salt concentration of 12.5% (w/v) during the second cultivation, the ectoine content was increased to 17 wt.% and productivity to 3.4 g L⁻¹ day⁻¹.     

Growth retardants stimulate guggulsterone production in the presence of fungal elicitor in fed-batch cultures of <Emphasis Type="Italic">Commiphora wightii</Emphasis>

Guggulsterone, a hypolipidemic natural agent, is produced in resin canals of the plant Commiphora wightii. In this study, the stimulatory effects of growth retardants [ALAR (N,N-dimethylaminosuccinamic acid) and CCC (chlormequat chloride)] and fungal elicitor on guggulsterone accumulation in cell cultures of C. wightii are reported. CCC at 1 mg l⁻¹ enhanced guggulsterone content (~123 μg l⁻¹) when added on the fifth day after inoculation, while ALAR at 2.5 mg l⁻¹ increased guggulsterone content (~116 μg l⁻¹) when added on the tenth day. In a two-stage fed-batch process, combined treatment with fungal elicitor and growth retardant caused a significant increase (~353 μg l⁻¹) in guggulsterone content in cell cultures after 17 days of growth. This represents an approximately fivefold increase over the guggulsterone contents in initial cultures of this plant.     

Xylitol production by recombinant Corynebacterium glutamicum under oxygen deprivation

Wild-type Corynebacterium glutamicum produced 0.6 g l⁻¹ xylitol from xylose at a productivity of 0.01 g l⁻¹ h⁻¹ under oxygen deprivation. To increase this productivity, the pentose transporter gene (araE) from C. glutamicum ATCC31831 was integrated into the C. glutamicum R chromosome. Consequent disruption of its lactate dehydrogenase gene (ldhA), and expression of single-site mutant xylose reductase from Candida tenuis (CtXR (K274R)) resulted in recombinant C. glutamicum strain CtXR4 that produced 26.5 g l⁻¹ xylitol at 3.1 g l⁻¹ h⁻¹. To eliminate possible formation of toxic intracellular xylitol phosphate, genes encoding xylulokinase (XylB) and phosphoenolpyruvate-dependent fructose phosphotransferase (PTS^fru) were disrupted to yield strain CtXR7. The productivity of strain CtXR7 increased 1.6-fold over that of strain CtXR4. A fed-batch 21-h CtXR7 culture in mineral salts medium under oxygen deprivation yielded 166 g l⁻¹ xylitol at 7.9 g l⁻¹ h⁻¹, representing the highest bacterial xylitol productivity reported to date.     

Statistical medium optimization for enhanced azadirachtin production in hairy root culture of Azadirachta indica

Azadirachtin, a well-known biopesticide, is a secondary metabolite extracted from the seeds of Azadirachta indica. In the present study, azadirachtin was produced in hairy roots of A. indica, generated by Agrobacterium rhizogenes-mediated transformation of leaf explants. Liquid cultures of A. indica hairy roots were developed with a liquid-to-flask volume ratio of 0.15. The kinetics of growth and azadirachtin production were established in a basal plant growth medium containing MS medium major and minor salts, Gamborg’s medium vitamins, and 30 g l⁻¹ sucrose. The highest azadirachtin accumulation in the hairy roots (up to 3.3 mg g⁻¹) and azadirachtin production (∼44 mg l⁻¹) was obtained on Day 25 of the growth cycle, with a biomass production of 13.3 g l⁻¹ dry weight. To enhance the production of azadirachtin, a Plackett–Burman experimental design protocol was used to identify key medium nutrients and concentrations to support high root biomass production and azadirachtin accumulation in hairy roots. The optimal nutrients and concentrations were as follows: 40 g l⁻¹ sucrose, 0.19 g l⁻¹ potassium dihydrogen phosphate, 3.1 g l⁻¹ potassium nitrate, and 0.41 g l⁻¹ magnesium sulfate. Concentrations were determined by a central composite design protocol and verified in shake-flask cultivation. The optimized medium composition yielded a root biomass production of 14.2 g l⁻¹ and azadirachtin accumulation of 5.2 mg g⁻¹, which was equivalent to an overall azadirachtin production of 73.84 mg l⁻¹, 68% more than that obtained under non-optimized conditions.     

Citric acid production from glycerol-containing waste of biodiesel industry by Yarrowia lipolytica in batch, repeated batch, and cell recycle regimes

Yarrowia lipolytica A-101-1.22 produces high citric acid (112 g l⁻¹) with a yield of 0.6 g g⁻¹ and a productivity of 0.71 g l⁻¹ h⁻¹ during batch cultivation in the medium with glycerol-containing waste of biodiesel industry. However, it was observed that the specific citric acid production rate, which was maximal at the beginning of the biosynthesis, gradually decreases in the late production phase and it makes continuation of the process over 100 h pointless. The cell recycle and the repeated batch regimes were performed as ways for prolongation of citric acid synthesis by yeast. Using cell recycle, the active citric acid biosynthesis (96–107 g l⁻¹) with a yield of 0.64 g g⁻¹ and a productivity of 1.42 g l⁻¹ h⁻¹ was prolongated up to 300 h. Repeated batch culture remained stable for over 1000 h; the RB variant of 30% feed every 3 days showed the best results: 124.2 g l^-1 citric acid with a yield of 0.77 g g^-1 and a productivity of 0.85 g l^-1 h^-1.     

Genetic modification of industrial yeast strains to obtain controllable NewFlo flocculation property and lower diacetyl production

The expression cassette I10 containing the new-found flocculation gene, FLONS, was transformed into an industrial strain Saccharomyces cerevisiae YSF5. Upstream activating sequences of the S. cerevisiae alcohol dehydrogenase II (ADH2) gene promoter (P_U-ADH2) were used to regulate the expression of FLONS; α-acetolactate synthase gene ILV2 was chosen for homologous recombination of I10 to the YSF5 chromosome; copper binding metallothionein (encoded by CUP1) was used for selection of transformants. Ten randomly selected transformants exhibited increased flocculation ability of 1.5 to 2.3 fold more than the original strain. Based on their sensitivity to glucose, maltose and sucrose, flocculation property of the transformants was supported to be NewFlo-type. After successive subculture, the introduced CUP1 remained in the transformants. At the end of simulated fermentation test, diacetyl content of the culture media of 5I-1 was 0.45 g l⁻¹, lower than YSF5 (0.48 g l⁻¹).     

Drift-ice and under-ice water communities in the Gulf of Bothnia (Baltic Sea)

The algal, protozoan and metazoan communities within different drift-ice types (newly formed, pancake and rafted ice) and in under-ice water were studied in the Gulf of Bothnia in March 2006. In ice, diatoms together with unidentified flagellates dominated the algal biomass (226 ± 154 μg ww l⁻¹) and rotifers the metazoan and protozoan biomass (32 ± 25 μg ww l⁻¹). The under-ice water communities were dominated by flagellates and ciliates, which resulted in lower biomasses (97 ± 25 and 21 ± 14 μg ww l⁻¹, respectively). The under-ice water and newly formed ice separated from all other samples to their own cluster in hierarchical cluster analysis. The most important discriminating factors, according to discriminant analysis, were chlorophyll-a, phosphate and silicate. The under-ice water/newly formed ice cluster was characterized by high nutrient and low chlorophyll-a values, while the opposite held true for the ice cluster. Increasing trends in chlorophyll-a concentration and biomass were observed with increasing ice thickness. Within the thick ice columns (>40 cm), the highest chlorophyll-a concentrations (6.6–22.2 μg l⁻¹) were in the bottom layers indicating photoacclimation of the sympagic community. The ice algal biomass showed additional peaks in the centric diatom-dominated surface layers coinciding with the highest photosynthetic efficiencies [0.019–0.032 μg C (μg Chl-a ⁻¹ h⁻¹) (μE m⁻² s⁻¹)⁻¹] and maximum photosynthetic capacities [0.43-1.29 μg C (μg Chl-a ⁻¹ h⁻¹)]. Rafting and snow-ice formation, determined from thin sections and stable oxygen isotopic composition, strongly influenced the physical, chemical and biological properties of the ice. Snow-ice formation provided the surface layers with nutrients and possibly habitable space, which seemed to have favored centric diatoms in our study.     

Carbon source pulsed feeding to attain high yield and high productivity in poly(3-hydroxybutyrate) (PHB) production from soybean oil using <Emphasis Type="Italic">Cupriavidus necator</Emphasis>

Poly(3-hydroxybutyrate) (PHB) biosynthesis from soybean oil by Cupriavidus necator was studied using a bench scale bioreactor. The highest cell concentration (83 g l⁻¹) was achieved using soybean oil at 40 g l⁻¹ and a pulse of the same concentration. The PHB content was 81% (w/w), PHB productivity was 2.5 g l⁻¹ h⁻¹, and the calculated Y_p/s value was 0.85 g g⁻¹. Growth limitation and the onset of PHB biosynthesis took place due to exhaustion of P, and probably also Cu, Ca, and Fe.     

Substrate specificity of a recombinant ribose-5-phosphate isomerase from <Emphasis Type="Italic">Streptococcus pneumoniae</Emphasis> and its application in the production of <Emphasis Type="SmallCaps">l</Emphasis>-lyxose and <Emphasis Type="SmallCaps">l</Emphasis>-tagatose

A putative ribose-5-phosphate isomerase (RpiB) from Streptococcus pneumoniae was purified with a specific activity of 26.7 U mg⁻¹ by Hi-Trap Q HP anion exchange and Sephacryl S-300 HR 16/60 gel filtration chromatographies. The native enzyme existed as a 96-kDa tetramer with activity maxima at pH 7.5 and 35°C. The RpiB exhibited isomerization activity with l-lyxose, l-talose, d-gulose, d-ribose, l-mannose, d-allose, l-xylulose, l-tagatose, d-sorbose, d-ribulose, l-fructose, and d-psicose and exhibited particularly high activity with l-form monosaccharides such as l-lyxose, l-xylulose, l-talose, and l-tagatose. With l-xylulose (500 g l⁻¹) and l-talose (500 g l⁻¹) substrates, the optimum concentrations of RpiB were 300 and 600 U ml⁻¹, respectively. The enzyme converted 500 g l⁻¹ l-xylulose to 350 g l⁻¹ l-lyxose after 3 h, and yielded 450 g l⁻¹ l-tagatose from 500 g l⁻¹ l-talose after 5 h. These results suggest that RpiB from S. pneumoniae can be employed as a potential producer of l-form monosaccharides.     

Selection of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> strains for efficient very high gravity bio-ethanol fermentation processes

An optimized very high gravity (VHG) glucose medium supplemented with low cost nutrient sources was used to evaluate bio-ethanol production by 11 Saccharomyces cerevisiae strains. The industrial strains PE-2 and CA1185 exhibited the best overall fermentation performance, producing an ethanol titre of 19.2% (v/v) corresponding to a batch productivity of 2.5 g l⁻¹ h⁻¹, while the best laboratory strain (CEN.PK 113-7D) produced 17.5% (v/v) ethanol with a productivity of 1.7 g l⁻¹ h⁻¹. The results presented here emphasize the biodiversity found within S. cerevisiae species and that naturally adapted strains, such as PE-2 and CA1185, are likely to play a key role in facilitating the transition from laboratory technological breakthroughs to industrial-scale bio-ethanol fermentations.     

Effects of acetic acid, ethanol, and SO2 on the removal of volatile acidity from acidic wines by two Saccharomyces cerevisiae commercial strains

Herein, we report the influence of different combinations of initial concentration of acetic acid and ethanol on the removal of acetic acid from acidic wines by two commercial Saccharomyces cerevisiae strains S26 and S29. Both strains reduced the volatile acidity of an acidic wine (1.0 g l⁻¹ acetic acid and 11% (v/v) ethanol) by 78% and 48%, respectively. Acetic acid removal by strains S26 and S29 was associated with a decrease in ethanol concentration of 0.7 and 1.2% (v/v), respectively. Strain S26 revealed better removal efficiency due to its higher tolerance to stress factors imposed by acidic wines. Sulfur dioxide (SO₂) in the concentration range 95–170 mg l⁻¹ inhibits the ability of both strains to reduce the volatile acidity of the acidic wine used under our experimental conditions. Therefore, deacidification should be carried out either in wines stabilized by filtration or in wines with SO₂ concentrations up to 70 mg l⁻¹. Deacidification of wines with the better performing strain S26 was associated with changes in the concentration of volatile compounds. The most pronounced increase was observed for isoamyl acetate (banana) and ethyl hexanoate (apple, pineapple), with an 18- and 25-fold increment, respectively, to values above the detection threshold. The acetaldehyde concentration of the deacidified wine was 2.3 times higher, and may have a detrimental effect on the wine aroma. Moreover, deacidification led to increased fatty acids concentration, but still within the range of values described for spontaneous fermentations, and with apparently no negative impact on the organoleptical properties.     

Fermentation of high concentrations of lactose to ethanol by engineered flocculent Saccharomyces cerevisiae

The development of microorganims that efficiently ferment lactose has a high biotechnological interest, particularly for cheese whey bioremediation processes with simultaneous bio-ethanol production. The lactose fermentation performance of a recombinant Saccharomyces cerevisiae flocculent strain was evaluated. The yeast consumed rapidly and completely lactose concentrations up to 150 g l⁻¹ in either well- or micro-aerated batch fermentations. The maximum ethanol titre was 8% (v/v) and the highest ethanol productivity was 1.5–2 g l⁻¹ h⁻¹, in micro-aerated fermentations. The results presented here emphasise that this strain is an interesting alternative for the production of ethanol from lactose-based feedstocks.     

Dynamic microbial response under ethanol stress to monitor <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> activity in different initial physiological states

Dynamic Saccharomyces cerevisiae responses to increasing ethanol stresses were investigated to monitor yeast viability and to optimize bioprocess performance when gradients occurred due to the specific configuration of multi-stage bioreactors with cell recycling or of large volume industrial bioreactors inducing chemical heterogeneities. Twelve fed-batch cultures were carried out with initial ethanol concentrations (P _in) ranging from 5 g l⁻¹ to 110 g l⁻¹ with three different inoculums in different physiological states in terms of viability and quantity of ethanol produced (P _o). For a given initial cell viability of 50%, the time to reach the maximum growth rate and maximum ethanol production rate was dependent on the difference P _in − P _o. Whatever the initial physiological state, when the initial ethanol concentration P _in reached 100 g l⁻¹, the yeasts died. Experimental results showed that the initial physiological state of the yeast was the major parameter to determine, the microorganisms’ capacities to adapt and resist environmental changes.     

Isolation of <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> mutants for heterologous protein production from a double proteinase gene disruptant

The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l⁻¹ h⁻¹, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition strategy, which reached 8.46 ± 0.31 g l⁻¹, 41.7 ± 1.4%, and 0.18 ± 0.01 g l⁻¹ h⁻¹ with the best continuous feeding strategy (0.2 g l⁻¹ h⁻¹), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L⁻¹ h⁻¹) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when the l-Met feeding rate reached 0.5 g l⁻¹ h⁻¹.     

Abundance and composition of the summer phytoplankton community along a transect from the Barguzin River to the central basin of Lake Baikal

The abundance and composition of phytoplankton were investigated at six stations along a transect from the Barguzin River inflow to the central basin of Lake Baikal in August 2002 to clarify the effect of the river inflow on the phytoplankton community in the lake. The water temperature in the epilimnion was high near the shore at Station 1 (17.3°C), probably due to the higher temperature of the river water, and gradually decreased offshore at Station 6 (14.5°C). Thermal stratification developed at Stations 2–6, and a thermocline was observed at a 17–22-m depth at Stations 2–4 and an 8–12-m depth at Stations 5 and 6. The concentrations of nitrogen and phosphorus nutrients in the epilimnion at all stations were <1.0 μmol N l⁻¹ and <0.16 μmol P l⁻¹, respectively. Relatively high concentrations of nutrients (0.56–7.38 μmol N l⁻¹ and 0.03–0.28 μmol P l⁻¹) were detected in the deeper parts of the euphotic zone. Silicate was not exhausted at all stations (>20 μmol Si l⁻¹). The chlorophyll a (chl. a) concentration was high (>10 μg l⁻¹) near the shore at Station 1 and low (<3 μg l⁻¹) at five other stations. The <2 μm fraction of chl. a in Stations 2–6 ranged between 0.80 and 1.85 μg l⁻¹, and its contribution to total chl. a was high (>60%). In this fraction, picocyanobacteria were abundant at all stations and ranged between 5 × 10⁴ and 5 × 10⁵ cells ml⁻¹. In contrast, chl. a in the >2 μm fraction varied significantly (0.14–11.17 μg l⁻¹), and the highest value was observed at Station 1. In this fraction, the dominant phytoplankton was Aulacoseira and centric diatoms at Station 1 and Cryptomonas, Ankistrodesmus, Asterionella, and Nitzschia at Stations 2–6. The present study demonstrated the dominance of picophytoplankton in the pelagic zone, while higher abundance of phytoplankton dominated by diatoms was observed in the shallower littoral zone. These larger phytoplankters in the littoral zone probably depend on nutrients from the Barguzin River.     

Fed-batch production of a bioflocculant from <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>

The constant-rate fed-batch production of the polygalacturonic acid bioflocculant REA-11 was studied. A controlled sucrose-feeding strategy resulted in a slight improvement in biomass and a 7% reduction in flocculating activity compared with the batch process. When fed with a 3 g l⁻¹ urea solution, the flocculating activity was enhanced to 720 U ml⁻¹ in 36 h. High cell density (2.12 g l⁻¹) and flocculating activity (820 U ml⁻¹) were obtained in a 10-l fermentor by feeding with a sucrose-urea solution, with values of nearly two times and 50% higher than those of the batch process, respectively. Moreover, the residual sucrose declined to 2.4 g l⁻¹, and residual urea decreased to 0.03 g l⁻¹. Even higher flocculating activity of 920 U ml⁻¹ and biomass of 3.26 g l⁻¹ were obtained by feeding with a sucrose-urea solution in a pilot scale fermentation process, indicating the potential industrial utility of this constant-rate feeding strategy in bioflocculant production by Corynebacterium glutamicum.